The Metamorphosis is an argueably nihilist work by Franz Kafka about an ordinary man who turns into a giant insect, and how his transformation affects his family life.
One of the major changes Gregor suffers is to his voice; no longer able to communicate as a human, he strives to make his new insect voice audible to his family. It seems at first that his voice is the last thing to change; after waking, Gregor communicates (sight unseen) with his family and is upset to discover that his voice has started to deteriorate, with an unintelligible squeaking overpowering his articulation. After his revelation, Gregor makes a speech explaining his desire to go to work, but it is unclear how much, if any, is intelligible.
It was clearly and unmistakably his earlier voice, but in it was intermingled, as if from below, an irrepressibly painful squeaking...
"For God's sake," cried the mother, already in tears. "Perhaps he's very ill, and we're upsetting him." [...] "Have you heard Gregor speak yet?" "That was an animal's voice," said the attorney.
(Kafka, The Metamorphosis, eNotes eText)
Gregor's voice is perhaps the last vestige of his true humanity, as after his family understands his transformation, they treat him entirely as an unintelligent creature rather than as their relative. The only time someone truly shows Gregor compassion is after his father attacks him with apples, and his sister, understanding that Gregor is still her brother, defends him. Gregor stops trying to communicate and begins to accept his role as an animal; his voice, one of the defining factors of sentient creatures, is the last thing with which he defends his humanity. When Gregor's voice fails, his humanity similarly ends, and his family abandons their worry and care in favor of disgust.